The purpose of this investigation is to solubilize, purify, isolate and characterize tumor rejection antigens from immunogenic mouse melanoma and mammary adenocarcinoma cells. The melanoma cells were rendered nontumorigenic and immunogenic by long term culture in 1 microgram/ml of bromodeoxyuridine and the mammary tumor cells by long term culture in normal medium. Plasma membranes will be isolated by differential centrifugation from cells disrupted by nitrogen cavitation and fractionated on sucrose-dextran and sucrose flotation gradients. Characteristics of the purified subcellular fractions will be monitored by radioimmune and biochemical assays. Immunogenicty will be tested both by in vivo tumor rejection assays and by in vitro assays worked out with whole cells. Soluble fractions will be prepared from the immunogenic fraction and purified by apropriate chromatographic methods. Immunochemical analysis of the membrane fractions will be carried out using antisera we have prepared. Biochemical studies on the glycosaminoglycans and proteoglycans of these cells will be made and correlated with their unusual biological properties. The ultimate aim of these studies is to use them as model systems forming a basis for safe immunization of melanoma and breast cancer patients after removal of their primary tumors.